702 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. 



Slags are not scorije. They do uot belong to the type of glasses, since they are 

 opaque ' and crystalline. They are uot artificial minerals, since they contain large 

 quantities of sulphurets. Instead of belonging to some well-known type, they form 

 one. It is only after a careful study of their nature and properties that it will be pos- 

 sible to attempt to give a satisfactory definition of these products. 



Properties of slag 1. Pulverized slag treated with the magnet almost always 



shows the presence of a magnetic portion which adheres strongly to the magnet. A 

 slag beautifully crystallized in detached rhomboidal laminae, with a steel-gray color 

 and an almost metallic luster, from the La Plata smelter, could be separated by the 

 magnet into two portions. 



Parts. 



A strongly maguetic portion, amounting to - 38 



A feebly magnetic portion, amounting to 62 



100 



But a rough examination, both quantitative and qualitative, of these two portions 

 showed no great difference in the composition, and the investigation was carried no 

 further in this direction. 



2. The same slag finely pulverized^ and treated by weak sulphuric acid (acid 1, 

 water 4) is rapidly attacked. Sulphureted hydrogen is evolved, showing the presence 

 of sulphides easily attacked by weak acids. The slag is, moreover, thoroughly disin- 

 tegrated after a few hours. A large proportion of silica, iron, lime, magnesia, man- 

 ganese, and zinc is dissolved. An uuattacked residue is left ; it is treated with weak 

 nitric acid, which dissolves some sulphide of lead, formed evidently during the reac- 

 tion, for it has the aspect of artificial sulphide of lead formed in the wet way. The 

 residue is then boiled with carbonate of soda, which dissolves some gelatinous silica. 

 A residue is still left ; it is attacked a second time by weak sulphuric acid, weak nitric 

 acid, and carbonate of soda. It is interesting to observe that after each successive 

 treatment sulphureted hydrogen is evolved, showing that the sulphides are undoubt- 

 edly combined with silica or with silicates. After each treatment, silica, iron, lime, etc., 

 are dissolved. These treatments are repeated until the residue cou.sists of intensely 

 black, fine, brilliant crystals. It is formed of pure magnetic oxide of iron, which is 

 resolved into octahedra under the microscope. This oxide was analyzed; it con- 

 tained — 



Protoxide of iron — 40. 3 



Peroxide of iron 59. 7 



Its formula is FcTOg^SFeO, 2Fe303, instead of Fe608=2FeO, 2Fe203=2Fe304, the for- 

 mula of ordinary magnetite. It contains one equivalent of protoxide of iron more 

 than normal magnetite. In hematite has been seen a magnetite containing an excess 

 of peroxide of iron ; here is found a magnetite formed in the midst of jirotoxide of iron 

 and containing an excess of this oxide. 



1 The opacity of some slags is sucli that thin sections, prepared by Mr. Whitman Cross for micro- 

 scopical examination, proxed totally opaque, even under the microscope. 

 'Sifted slag is also very easily attacked by weak acids. 



